HONOLULU (AP) — The accidental introduction of a snake species to Guam several decades ago almost completely wiped out the Pacific island's forest birds. Now, the lack of birds is causing Guam's spider population to explode.
A new study shows Guam's jungles have 40 times more spiders in the wet season than the jungles of the nearby islands of Rota, Saipan and Tinian, where birds are still around to eat spiders.
During the dry season, Guam — a U.S. territory about 1,500 miles south of Tokyo and 3,700 miles southwest of Hawaii — had more than twice as many spiders as the nearby islands.
Haldre Rogers, lead author of the study published this month online in the journal PLOS ONE, and fellow researchers measured sections of jungle about 65 to 100 feet long and counted the number of spider webs with spiders in these areas. The used the same type of forest — limestone — for the study on each island.
"When we did all these surveys on the other islands it didn't take any time at all. You got your transect tape and you counted spiders and there weren't very many and it was very quick," said Rodgers, a faculty fellow at Rice University. "Then we got to Guam, and each survey just took forever because there were so many more spiders."
Webs woven by one species — argiope appensa or garden spider — were also 50 percent larger on Guam, the study found. This suggests the garden spider is able to keep its webs up longer or build larger webs when birds aren't around, Rogers said.
Rogers said she did the study after anecdotally observing that Guam had more spiders. But she didn't expect to the research to show such a large difference.
Guam's forest birds were almost completely eliminated by the brown tree snake, a reptile native to Australia and the Solomon Islands that doesn't have any natural predators on the island. It's not known how brown tree snakes arrived on Guam, though most likely they stowed away on a cargo ship after World War II.
Hawaii officials have long been concerned the snakes might sneak onto cargo leaving Guam and do the same thing to birds in the 50th state that they did to Guam's avian species.
Rogers doesn't want to people to get the mistaken impression that Guam is coated in spider webs. Spiders are abundant in the jungle, but people wouldn't notice them elsewhere any more than they would in other places.
So there's no need for those who fear spiders to stay away from the tropical island popular with vacationers from Japan, South Korea and Asian nations.
"Arachnophobes should avoid the jungles of Guam. But they can still go and snorkel and dive and do their duty free shopping like most of the tourists do," Rogers said.